Detection and measurement of vibrational dynamics including displacements and velocities on the surface of a vibrating component part is important in many applications such as, for example, the testing of critical structural elements of submarine hulls, aircraft fuselages, aircraft wings, and in surface acoustic wave (SAW) electronic devices, material characterization, and the like. It is most desirable during such detection that the measurement method be non-intrusive such that the measurement device itself does not affect any motion in the part being tested.
Through the years, various methods and devices have been developed to detect and measure vibration induced dynamics in a non-intrusive way. Most of these methods involve the use of coherent laser light that is reflected off of the vibrating surface with the reflected light being analyzed to extract information about the movement of the surface. In the device disclosed in U. S. Pat. No. 5,098,698 of Grego, for example, a reference beam of light and a frequency modulated beam are directed onto a surface and the combined reflected beam is heterodyne detected and analyzed to extract information about the movement of the surface. U.S. Pat. No. 4,907,886 of Dandliker discloses a method and device for use in range finding. The method of this patent involves directing two coherent beams of light having different frequencies to the surface of an object. Changes in the range of the object can then be determined by analyzing the phase changes that occur in the combined beam that is reflected from the object. Other patents that relate to this technology include U.S. Pat. No. 4,569,588 of Nishiwaki, U.S. Pat. No. 4,927,263 of de Groot et al., U.S. Pat. No. 5,070,483 of Berni, and U.S. Pat. No. 5,109,362 of Berni.
While previous methods and devices such as those discussed above represent innovation in the measurement of surface wave dynamics and have been somewhat successful in that regard, they nevertheless are plagued with various problems and shortcomings inherent in their respective designs and methodologies. Among the most critical of these shortcomings resides in the fact that such devices measure displacement and velocity of an object in only one direction. In range finding devices, for example, displacement and velocity is measured along the axis of the incident light beams. Seismic sensing devices for detecting tectonically induced motion of the ground measure movement of the ground in only one direction, usually vertically. The scope of the prior art does not include a reliable and accurate method and device for detecting and measuring vector dynamics, that is, displacements and velocities along more than one axis on the surface of a object that may be vibrating in random directions. There is thus a continuing and heretofore unaddressed need for such a method and apparatus and it is to the fulfillment of this need that the present invention is primarily directed.